There has been much debate in the guitar community about the quality and relative usefulness of tube-based pedals. While guitar players have been conditioned for years to believe that anything with tubes must automatically sound better than any similar thing without tubes, the truth is that all valve-based circuits are not equal. For one thing, most of the lively, complex, delicious tone and feel that we associate with a good tube amp emanates from the saturation of the amplifier's power tubes, rather than its preamp tubes. Tube preamp distortion—without the benefit of equal or greater amounts of power tube distortion to go with it—can be as gritty and unappealing as any ugly solid-state grind. Tube drive and distortion pedals function much like a tube preamp, and typically use the same 12AX7/ECC83 type tubes, so obviously a pedal with one little 12AX7 in it cannot possibly approximate the tone of, say, a quartet of raging EL34's. Another criticism of tube pedal designs is that, in many of them, the tube is essentially just decoration. It sees very little actual voltage and plays little or no part in the sound of the pedal. Because these tubes often don't glow in the context of a pedal circuit, some companies put an orange LED behind them to give players the illusion of a fiery bottle of tone sitting at their feet, furthering the deception.
Tube stompboxes also have a somewhat deserved reputation for being more expensive, noisy, and delicate than their solid-state brethren, when many of these solid-state pedals are capable of sounding just as good or better, making one wonder whether tube-based pedal designs are worth the trouble, or are little more than marketing gimmicks. All of these criticisms leveled at valve-based pedals are valid and contain some measure of truth, but in spite of this, there are at least a handful of tube tone boxes that are universally regarded as classics. How much the tiny tubes in these pedals' hearts influence their sound, I cannot say with authority, but they do sound fabulous either way. Here are a few of my favorite fire bottle-powered stompboxes:
BK Butler Tube Driver
The BK Butler Tube Driver has a sordid manufacturing history, having been made at various times and various places under both the Tube Works and Chandler names, before finally being produced in original form again by Butler himself, via his company, Butler Audio. The Tube Driver is legendary mostly because of its association with David Gilmour, who has used two of them on his board since the early 1990's and his work on Pink Floyd's Division Bell. Eric Johnson, Joe Satriani, and Billy Gibbons have also done their part to canonize the Tube Driver's huge, dynamic overdrive and boost tones. The Tube Driver is well-suited to tube swaps, sounding mellower and somewhat more compressed with a 12AU7, rather than the stock 12AX7. It also performs best with clean, high-wattage amplifiers with plenty of headroom (such as the Hiwatt amps that Mr. Gilmour pairs his with). Butler Audio sells its handmade, original Tube Driver direct for $299.
Ibanez Tube King TK999US
The original Ibanez Tube King overdrive was a very different beast than the reissued version in the red diamond-shaped box, which seems to be a rather bland, metal-oriented high gain distortion. In fact, the original Tube Kings were just a slight variation on the BK Butler Tube Driver, designed and built by Butler himself, for Ibanez, in Denver. Later versions were manufactured by Ibanez in Japan and featured a high quality noise suppression circuit, but otherwise were identical to the originals. The Tube King has a similarly big, amp-like tone as Butler's Tube Driver, with perhaps slightly more gain available. The original 12AX7 in these can be a tad harsh, but swapping it out for a lower gain 12AU7 or 12AT7 makes a considerable improvement in the Tube King's overall tone and noise floor. Original Tube Kings are a relative bargain on the used market, and can be had for between 100 and 150 dollars.
Effectrode PC-2A Compressor
Effectrode, out of Corvallis, Oregon, offers a full range of beautiful, tube-based preamps and effects units, including phasers, vibes, and tremolo pedals, but their PC-2A tube compressor stands out simply because it is the most transparent, natural sounding compressor pedal on the planet. It is on par with the pro audio units one would find in a rack at any professional recording studio, but in a compact pedal format. It uses military-grade, subminiature tubes and an optocoupler to produce sweet, warm compression and gentle limiting that fattens the tone without squashing the life out of it. It can be used as a compressor, a peak limiter, or, with the Peak control dialed back and the gain up, as a superb tube-powered boost. The PC-2A is expensive, at around $339, but if you want the best, it's definitely the one.
Hughes & Kettner Tube Rotosphere
The H&K Tube Rotosphere is a classic, 12AX7-powered Leslie rotating speaker simulator, used by everyone from Jeff Beck and Warren Haynes to Charlie Hunter, as well as many, many organists who would prefer to avoid toting around a real Leslie cabinet. Its thick, juicy warble is nearly indistinguishable from the real thing, and it features all the same functions as an actual Leslie, including a breaker switch for momentarily halting the rotors. The Tube Rotosphere is out of production at the moment, but both MkI and MkII versions are highly regarded, and are available on the used market for around 300 to 350 dollars.
Electro-Harmonix Wiggler
EHX has a number of tube-based pedal designs in its diverse and formidable lineup. Some are better than others, and one of the better ones is the Wiggler, a dual 12AX7WB-powered aluminum behemoth that makes a variety of dirty and (as advertised) wiggly sounds. It does a rad tremolo, a decent Leslie impression, and several varieties of vintage-style vibrato. It can also whip up some wonderfully nasty tube grime to go along with the wiggles. The Wiggler, like many EHX pedals, is a rather quirky piece of work, and it's also not the quietest pedal around, but for guitarists looking for something truly gross and throbby, it is well worth checking out. The Wiggler sells new for around 200 bucks.
Depsite the controversy surrounding the relative value of tube-based effect pedals, it's clear that many tube-based designs have proven their worth over time, with several highly reputable companies, such as Hughes & Kettner and Effectrode, choosing to specialize in these designs. As with all things in the music and guitar realm, ignore the hype and just use your ears.